Vertical (and/or short) takeoff and landing (VTOL) electric aircraft may use a plurality of lift fans, powered by electric motors, to take off, hover, and/or land. After takeoff and transition to forward flight, one or more propellers optimized for forward flight may be used. During takeoff and transition to forward flight, for example, typically on the order of 60 seconds or less, the power electronics of the lift motor controllers may dissipate several kilowatts of waste heat. Once the vehicle is flying, the lift motors may no longer be used until the aircraft lands (typically at least several minutes after takeoff).
In a typical electric vehicle, such as an electric car, the motor controllers would be cooled with a heat sink that directly transfers the waste heat to the ambient air. Alternatively, a liquid coolant can be used to transfer the heat away from the motor controllers, and then it is transferred to the ambient air using a radiator and fan. With both of these systems, the weight of the thermal management system can be substantial. If these typical approaches were used on an electric aircraft, they would have to be sized for the peak power dissipation (several kilowatts), even though that power dissipation happens over a relatively very short period of time. During takeoff, for example, the rate at which thermal energy is being dissipated may be quite large, although the total amount of thermal energy that is being dissipated is not very large.
As is generally true with aircraft, minimizing unnecessary weight can greatly increase performance, so minimizing the weight of components used to provide motor controller thermal management is advantageous.